1. Field of the Invention
The present invention relates to a method for manufacturing a magneto-electric conversion element which uses magnetism to detect the displacement of a moving object, and also to a displacement detector which uses a magneto-electric conversion device manufactured by that method that detects the displacement of a moving object.
2. Description of the Related Art
In the past, vehicle speed sensors, as shown in FIG. 14, included ferromagnetic magnetoresistive elements 31 formed by a thin film layer, such as Ni--Co or Ni--Fe, and an IC chip 32 onto which the ferromagnetic magnetoresistive elements 31 and a signal processing circuit of, for example, a bipolar transistor were provided. The IC chip 32 is located opposite a multipole magnet 33 which rotates along with the rotation of a drive gear. When the multipole magnet 33 rotates along with the drive gear, the change in magnetic flux detected by the ferromagnetic magnetoresistive element 31 is used to detect the rotation of the device gear.
However, the change in magnetic resistance of an Ni--Co or Ni--Fe element is 2 to 5%. As a result, when four ferromagnetic magneto-electric conversion devices are used to configure a bridge circuit, the S/N ratio of the intermediate voltage difference generated (offset voltage) drops. Also the thin film shown in FIG. 14 exhibits angle dependency with respect to magnetic flux A (horizontal vector magnetic flux). In order to obtain the maximum rate of change, it is necessary to determine the positioning of the multipole magnet 33 and IC chip 32 with high precision, thereby presenting a problem of high manufacturing cost.
To solve this problem, an object of the present invention is to provide a method of manufacturing a magneto-electric conversion device that not only has a high rate of change of magnetic resistance, but also provides easy alignment of the magneto-electric conversion device with respect to a magnetized surface and, in addition, to provide a moving object displacement detector formed using a magneto-electric conversion device manufactured by this method.